An AlGaInP based compound semiconductor light emitting diode can emit light with high efficiency in the wavelength region from red to yellow-green, and therefore, the use of the diode is expanded to the fields for a vehicle, traffic light and the like. Furthermore, the diode is used in combination with a GaN base compound semiconductor light emitting diode to prepare a white light emitting diode which can emit white light by emitting the three primary colors of blue, green and red.
The object of the AlGaInP based compound semiconductor light emitting diode is to improve the decrease in luminous efficiency and the deterioration in the case of extended drive, when the light emitting diode is intended to emit a light of a short wavelength region (from yellow to yellow-green).
The following reasons are cited as the factors which decrease luminous efficiency, wherein such a decrease of the luminous efficiency tends to be caused according as the wavelength becomes shorter.
(i) Carrier confinement becomes insufficient since the energy-gap difference between an emission layer and a cladding layer becomes small.
(ii) A non-luminescence center in the emission layer increases since Al composition
(aluminium ratio) in an emission layer becomes large.
(iii) Energy band structure approaches to an indirect transition type structure from a direct transition type structure.
In order to solve the problems, in Japanese Patent No. 3373561 (hereinafter, it is described as Patent document 1), a method is disclosed wherein a non-emission level in an emission layer is decreased by decreasing Al composition in the emission layer so that the emission layer has a quantum well structure having ten to eighty layers. Furthermore, in Japanese Patent No. 3732626 (Hereinafter, it is described as Patent document 2), a method for increasing luminous efficiency is disclosed wherein Zn is doped in an emission layer so that a non-luminescence center caused by impurities such as Si and the like is inactivated.    Patent document 1: Japanese Patent No. 3373561    Patent document 2: Japanese Patent No. 3732626